As the world's population expands and its economy increases, the atmospheric concentrations of carbon dioxide are warming the earth causing climate change. However, the global energy system is moving steadily away from the carbon-rich fuels whose combustion produces the harmful gas. Experts say atmospheric levels of carbon dioxide may double the end of the next century, and could be much higher except for a continuing trend toward lower-carbon fuels. Furthermore, fossil fuels generate many other pollutants and are a causative factor in many strategic military struggles between nations.
For nearly a century and a half, fuels with high amounts of carbon/energy have progressively been replaced by those containing smaller amounts of carbon. Wood, which is high in carbon, was eclipsed in the late 19th century by coal, which provides more energy. Then oil, with a lower carbon content still, dethroned “King Coal” in the 1960's. Now analysts say that natural gas, may be entering its heyday, and that the day of hydrogen—providing a fuel with no carbon at all—may at last be about to dawn. As a result, experts estimate the world's economy today burns less than two-thirds as much carbon per unit of energy produced as it did in 1860.
In the United States, it is estimated, that the trend toward lower-carbon fuels combined with greater energy efficiency has, since 1950, reduced by about half the amount of carbon spewed out for each unit of economic production. Thus, the decarbonization of the energy system is the single most important fact to emerge from the last 20 years of analysis of the system. It had been predicted that this evolution will produce a carbon-free energy system by the end of the 21st century. The present invention shortens that period to a matter of years. In the near term, hydrogen will be used in fuel cells to power cars, trucks and industrial plants, just as it already provides power for orbiting spacecraft. But ultimately, hydrogen will provide a carbon-free fuel to cover all fuel needs.
As noted in recent newspaper articles, large industries, especially in America, have long been suspicious of claims that the globe is warming and have vociferously negated the science of climate change. Electric utilities have even tried to stoke fears among ordinary folk that international treaties on climate change would cut economic growth and cost jobs. Therefore, it is very encouraging that some of the world's biggest companies, such as Royal Dutch/Shell and BP Amoco, two large European oil firms, now state plainly what was once considered heresy: global warming is real and merits immediate action. A number of American utilities have vowed to find ways to reduce the harm done to the atmosphere by their power plants. The automotive industry, which is a substantial contributor to emissions of greenhouse gases and other pollutants (despite its vehicular specific reductions in emissions), has now realized that change is necessary as evidenced by their electric and hybrid vehicles.
Hydrogen is the “ultimate fuel.” It is considered by most to be “THE” fuel for the next millennium, and, it is inexhaustible. Hydrogen is the most plentiful element in the universe (over 95%) and was the first element created by the “Big-Bang.” Hydrogen can provide an inexhaustible, clean source of energy for our planet which can be produced by splitting water into hydrogen and oxygen. The hydrogen can be stored and transported in solid state form and form the basis of a HYDROGEN ECONOMY™, trademark of Energy Conversion Devices, Inc. For example, economical, lightweight, triple-junction amorphous silicon solar cells (an invention pioneered by Stanford R. Ovshinsky, one of the instant inventors) such as those set forth in U.S. Pat. No. 4,678,679, (the disclosure of which is herein incorporated by reference) can be readily disposed adjacent a body of water, where their inherently high open circuit voltage can be used to dissociate water into its constituent gases, and collect the hydrogen so produced. Also, by placing these high efficiency solar panels on nearby farms, in water, or on land, electricity can be generated to transport and pump hydrogen into storage beds or tanks. These beds or tanks may include the inventive metal hydride alloys as disclosed herein, as well as others. The capacities of these alloys allow hydrogen to be stored in solid form for transport by barge, tanker, train or truck in safe, economical form for ultimate use. Energy is the basic necessity of life and civilization for any society today, and the use of hydrogen in the manner described herein as the basic source of energy could end wars fought for control of fossil fuels. Instead of “from well to wheel,” the phrase now recited will be “from source to wheel.”
In the past considerable attention has been given to the use of hydrogen as a fuel or fuel supplement. While the world's oil reserves are depletable, the supply of hydrogen remains virtually unlimited. Hydrogen can be produced from coal, natural gas and other hydrocarbons, or formed by the electrolysis of water. Electrolysis may be performed using energy from the sun which is composed mainly of hydrogen and can itself be thought of as a giant hydrogen “furnace”. Moreover hydrogen can be produced without the use of fossil fuels, such as by the electrolysis of water using nuclear or solar energy, or any other form of economical energy (e.g. wind, waves, geothermal, etc.). Furthermore, hydrogen, although presently more expensive than petroleum, is an inherently low cost fuel. Hydrogen has the highest density of energy per unit weight of any chemical fuel and is essentially non-polluting since the main by-product of “burning” hydrogen is water. Thus, hydrogen can be a means of solving many of the world's energy related problems, such as climate change, pollution, strategic dependency on oil, etc., as well as providing a means of helping developing nations.
While hydrogen has wide potential application as a fuel, a major drawback in its utilization, especially in mobile uses such as the powering of vehicles, has been the lack of acceptable lightweight storage medium. Conventionally, hydrogen has been stored in pressure-resistant vessels under a high pressure or stored as a cryogenic liquid, being cooled to an extremely low temperature. Storage of hydrogen as a compressed gas or liquid involves the use of large and heavy vessels, making the use of hydrogen to power vehicles less feasible.
Alternatively, certain metals and alloys have been known to permit reversible storage and release of hydrogen. In this regard, they have been considered as a superior hydrogen-storage material, due to their high hydrogen-storage efficiency. Storage of hydrogen as a solid hydride can provide a greater volumetric storage density than storage as a compressed gas or a liquid in pressure tanks. Also, hydrogen storage in a solid hydride presents fewer safety problems than those caused by hydrogen stored in containers as a gas or a liquid. Some of these alloys are described in U.S. Pat. No. 6,193,919, entitled “High Storage Capacity Alloys Enabling a Hydrogen-based Ecosystem”, which is hereby incorporated by reference.
With these developments in the storage of hydrogen, hydrogen now has a viable use as a fuel to power vehicles. Solid-phase metal or alloy systems can store large amounts of hydrogen by absorbing hydrogen with a high density and by forming a metal hydride under a specific temperature/pressure or electrochemical conditions, and hydrogen can be readily released by changing these conditions.
With hydrogen now being a viable source to power vehicles, considerable research has been performed on designing vehicles to run on hydrogen rather than fossil fuels. In these designs, hydrogen may be combusted inside an internal combustion engine or reacted in a fuel cell to power a vehicle. Such vehicles provide clean alternatives to internal combustion engines in widespread use today which utilize fossil fuels.
A fuel cell is an energy-conversion device that directly converts the energy of a supplied gas into electric energy. Researchers have been actively studying fuel cells to utilize the fuel cell's potential high energy-generation efficiency. The base unit of a fuel cell includes an oxygen electrode, a hydrogen electrode, and an appropriate electrolyte. Fuel cells have many potential applications such as supplying power for transportation vehicles, replacing steam turbines and power supply applications of all sorts. Despite their seeming simplicity, many problems have prevented the widespread usage of fuel cells.
Presently most of the fuel cell R & D focus is on P.E.M. (Proton Exchange Membrane) fuel cells. The P.E.M. fuel cell suffers from relatively low conversion efficiency and has many other disadvantages. For instance, the electrolyte for the system is acidic. Thus, noble metal catalysts are the only useful active materials for the electrodes of the system. Unfortunately, not only are the noble metals costly, they are also susceptible to poisoning by many gases, and specifically carbon monoxide (CO). Also, because of the acidic nature of the P.E.M fuel cell, the remainder of the materials of construction of the fuel cell need to be compatible with such an environment, which again adds to the cost thereof. The proton exchange membrane itself is quite expensive, and because of its low conductivity, inherently limits the power performance and operational temperature range of the P.E.M. fuel cell (the PEM is nearly non-functional at low temperatures, unlike the fuel cell of the instant invention). Also, the membrane is sensitive to high temperatures, and begins to soften at 120° C. The membrane's conductivity depends on water and dries out at higher temperatures, thus causing cell failure. Therefore, there are many disadvantages to the P.E.M. fuel cell which make it somewhat undesirable for commercial/consumer use.
The conventional alkaline fuel cell has some advantages over P.E.M. fuel cells in that they have higher operating efficiencies, they use less expensive materials of construction, and they have no need for expensive membranes. The alkaline fuel cell also has relatively higher ionic conductivity in the electrolyte, therefore it has a much higher power capability. Unfortunately, conventional alkaline fuel cells still suffer from certain disadvantages. For instance, conventional alkaline fuel cells still use expensive noble metals catalysts in both electrodes, which, as in the P.E.M. fuel cell, are susceptible to gaseous contaminant poisoning. While the conventional alkaline fuel cell is less sensitive to temperature than the PEM fuel cell, the active materials of conventional alkaline fuel cell electrodes become very inefficient at low temperatures.
Fuel cells, like batteries, operate by utilizing electrochemical reactions. Unlike a battery, in which chemical energy is stored within the cell, fuel cells generally are supplied with reactants from outside the cell. Barring failure of the electrodes, as long as fuel, such as hydrogen, and oxygen, is supplied and the reaction products are removed, the cell continues to operate.
Fuel cells offer a number of important advantages over internal combustion engine or generator systems. These include relatively high efficiency, environmentally clean operation especially when utilizing hydrogen as a fuel, high reliability, few moving parts, and quiet operation. Fuel cells potentially are more efficient than other conventional power sources based upon the Carnot cycle.
In a typical fuel cell, reactants, such as hydrogen and oxygen, are respectively fed through a porous hydrogen electrode and oxygen electrode and brought into surface contact with the electrolytic solution. The particular materials utilized for the hydrogen electrode and oxygen electrode are important since they must act as efficient catalysts for the reactions taking place.
The reaction at the hydrogen electrode occurs between the hydrogen fuel and hydroxyl ions (OH−) present in the electrolyte, which react to form water and release electrons:H2+2OH−→2H2O+2e−.At the oxygen electrode, oxygen, water, and electrons react in the presence of the oxygen electrode catalyst to reduce the oxygen and form hydroxyl ions (OH−):O2+2H2O+4e−→4OH−.The flow of electrons is utilized to provide electrical energy for a load externally connected to the hydrogen and oxygen electrodes.
To provide vehicles with extended range and higher power, systems have been developed wherein a hydrogen internal combustion engine (ICE) operates in conjunction with a battery to power a vehicle. Such systems are termed “Hybrid Systems”. An example of this type of system is disclosed in U.S. Pat. No. 6,330,925, entitled “Hybrid Electric Vehicle Incorporating An Integrated Propulsion System”, the disclosure of which is herein incorporated by reference.
Hybrid systems have been divided into two broad categories, namely series and parallel systems. In a typical series system, a battery powers an electric propulsion motor which is used to drive a vehicle and an internal combustion engine is used to recharge the battery. In a parallel system, both the internal combustion engine and the battery power in conjunction with an electric motor can be used, either separately or together, to power a vehicle. In these types of vehicles, the battery is usually used only in short bursts to provide increased power upon demand after which the battery is recharged using the internal combustion engine or regenerative braking.
There are further variations within these two broad categories. One variation is made between systems which are “charge depleting” in the one case and “charge sustaining” in another case. In the charge depleting system, the battery charge is gradually depleted during use of the system and the battery thus has to be recharged periodically from an external power source, such as by means of connection to public utility power. In the charge sustaining system, the battery is recharged during use in the vehicle, through regenerative braking and also by means of electric power supplied from the a generator powered by the internal combustion engine so that the charge of the battery is maintained during operation.
There are many different types of systems that fall within the categories of “charge depleting” and “charge sustaining” and there are thus a number of variations within the foregoing examples which have been simplified for purposes of a general explanation of the different types. However, it is to be noted in general that systems which are of the “charge depleting” type typically require a battery which has a higher charge capacity (and thus a higher specific energy) than those which are of the “charge sustaining” type if a commercially acceptable driving range (miles between recharge) is to be attained in operation.
A key enabling technology for HEVs is having an energy storage system having a high energy density while at the same time being capable of providing very high power. Such a system allows of rrecapture of energy from braking currents at very high efficiency.
An example of such a battery has been demonstrated by the Ovonic Battery Company. The OVONIC™ Nickel Metal Hydride (NiMH) battery has reached an advanced stage of development for use in vehicles. OVONIC™ electric vehicle batteries are capable of not only high power but high energy as well as long cycle life, abuse tolerance, and rapid recharge capability.